The present invention relates to the formulation of compositions for cables filling used in telecommunication, more specifically it relates to the use in these compositions of a hydrogenated radial styrene-butadiene block copolymer.
The use of synthetic rubbers in the formulation of waterproof compounds used in communication cables filling is known, the aim of these synthetic rubbers is to act as gelling agents, effective in the formation of a crystalline structure stable during long storage periods and in different temperature conditions.
On the other hand, the cables filling compositions of the prior art formulated with synthetic rubber show an excellent behavior as an anti-humidity barrier, avoiding the penetration of contaminators and protecting the cable from the breaking due to mechanical efforts during its handling. Due to their suitable viscosity, they can be injected at low temperature, filling the interstices of the cable and giving to the final product characteristics suitable as a support of the wires.
Examples of this type of formulations can be found in different patents: EP 0749128, U.S. Pat. Nos. 5,358,664, 4,810,395, 5,348,669, EP 0236918 and WO 97/04465.
The formulation of these compositions is realized by using mainly refined mineral basis or synthetic basis with the addition of synthetic rubbers (usually hidrogenated), and optionally polyethylene waxes and anti-oxidant additives.
However, these formulations show the problem that they are very sensitive to the variations of the waxes used in the formulation. Especially the Drip-Test value, that calculates the gel stability in time and at different temperatures. So, for compositions with the same proportions of synthetic rubber, a change in crystallinity in the polyethylene wax can seriously affect the stability of these compounds.
As a consequence, there is the need of a composition for cables filling that shows improved stability over the compositions of the prior art.
It has been surprinsingly found that the use of a radial hydrogenated styrene-butadiene block copolymer in the formulation of cables filling compounds not only improves the Drip-Test values, but also substantially improves the stability of the compositions.
The invention concerns compositions for cables filling wherein a hydrogenated styrene-butadiene block copolymer with radial structure is used as a gelling agent. This polymer is obtained through styrene and butadiene sequential polymerization and subsequent reaction with a coupling agent preferably of type Cl4-nMRn, wherein M=Sn or Si, and hydrogenation of the resulting polymer.
The object of the present invention is the provision of compositions for cables filling that show an improved stability.
The composition for cables filling of the present invention is characterized by the use of a hydrogenated styrene-butadiene block copolymer with a radial structure (radial SEBS), obtained through coupling.
The composition comprises: from 70 to 90% of a mineral or synthetic oil, from 0 to 12% of a polyethylene wax, 2 to 15% of radial SEBS synthetic rubber.
The radial copolymer can be synthesized through known methods, for example by anionic polymerization catalyzed by butillithium. In this case, a polymer is prepared by sequential polymerization of a vinyl aromatic monomer (e.g. styrene) and a conjugated diene monomer (e.g. butadiene). A lithium atom ends the chain of the polymer. In this way it is possible to go on polymerizing or reacting with other compounds as in the case of a coupling agent. The coupling agents for polymer chains are known in the art, as for CO2, dihaloalcanes, divinylbenzene, carbonates, chlorides, etc. The use of agents, whose functionally is higher than two, allows the formation of radial polymers. The preferred coupling agents of the invention are of type Cl4-nMRn, wherein M=Sn or Si, R is an alkyl or aryl group and n is an integer from 0 to 2, and the most preferred are those having a theoretic functionality equal to four and more concretely Cl4Si or Cl4Sn.
The structure of the butadiene block has preferably a vinyl content sufficient so that, when hydrogenating the polymer, this continues to be soluble in the reaction medium and the resulting polymer maintains its elastomeric properties. More specifically the vinyl content is preferably higher than 25% more preferably higher than 30% and most preferably between 35 and 45% based on the polybutadiene fraction. A known method to achieve these percentages of vinyl addition is the use of polymerization polar modifiers known in the art, such as quaternary amines, ethers, etc.
The styrene content in the copolymer is preferably between 20 and 40%, more preferably between 25 and 35% of styrene.
The coupling percentage of the styrene butadiene chains is not a critical parameter, it should however be sufficient to give the properties of a radial polymer. Preferably more than 80% of the chains and more preferably more than 90% of the chains are coupled.
The polymer final molecular weight is such that the resulting composition viscosity is as low as possible in order to be easily injectable. For this reason the molecular weight of the polymer of the invention is preferably between 30,000 and 110,000 and more preferably between 60,000 and 90,000. A too low molecular weight would not give the desired properties without adding a higher quantity of polymer, thus increasing the cost of the formulation, while a too high molecular weight would lead to viscous formulations that are difficult to be injected at room temperature and would require a higher amount of energy.
The polymers hydrogenation can be done through the methods known in she art, more preferably by a homogeneous hydrogenation process, under moderate pressure and temperature conditions, that avoids breaking of the coupled polymer chains. More preferably a metallocene catalyst is used that does not require the step of separation of the catalyst from the polymer. The most preferred hydrogenation processes used in the present invention are those described in EP 0601953 and EP 0885905, though they do not limit the present invention.
Suitable oil to be used in the present invention are polybutene oils and mineral oils such as naphthenic oils and paraffinic oils, triglyceride based oils (such as castor oil), polypropylene and polypropylene glycol oils. It is also possible to use mixtures of the above oils. Preferred oils or oil compositions have a viscosity at 100xc2x0 C. between 2 and 6 cSt.
The composition can also comprise up to 12% by weight of a polyethylene wax. Preferred polyethylene waxes have a melting point comprised between 90 and 120xc2x0 C.
The composition can also comprise other components, such as antioxidants, dyes, fungus inhibitors.
In a preferred embodiment, the composition comprises from 0.05 to 0.4% by weight of an antioxidant.
What follows are some explanatory examples of the composition object the invention, that show the advantage of using radial SEBS as compared to linear SEBS sythetic rubbers. These examples do not imply any limitation of the scope of the invention.